help on bass absorper. will this be worthwhile?

[thethingwiththestuff]

hey all, figured i'd see what people might think of this idea.

i recently received my insulation order from ats acoustics. i got 6 2'X4' sheets of 2" OC 703 unfaced, and 12 sheets of mineral wool. i've got a partially-finished basement that was already sounding pretty good, and a bed/control room that was quite ringy. both are sounding much better already.

i'm mostly just making broadband absorbers (burlap spray-adhered to the material, hung by twine and hooks, no wood frames). i may make a deeper bass trap (sealed, wood front.....) in place of one panel of drywall.

so, there are three windows i want to cover up to reduce some transmission to the outside. i know, I KNOW that i cant soundproof it. there's very little noise heard at the front of the house and the back, but on the side where the windows are, its pretty present. the windows are pretty flimsy, looks like plastic sheets screwed into a wood frame stuck into the stone. the window cavity is just under 3'X3", and is recessed about 6" or so into the wall..

my plan is to caulk around the edges of the existing window. i will build a frame out from the existing one, just a thin, top, bottom, and sides of a box. half a sheet of mineral wool will be stuffed against the window and held there by some small shims or something. there will be another couple inches of air in front of the min. wool, and then a piece of plywood or mdf covering the open end of the "box" and screwed and caulked, etc. it won't be large, but it should be air tight and will have a plywood resonator , 2-3" of air, insulation, then thw windows.

might this provide a reasonable amount of absorption and prevent too much transmission to the outside? i wish i knew how to "draft" something to scale on a computer.

thanks

[philbo]

Absorption is not going to help you with sound transmission, but it will make your room sound better due to absorbing reflections that would otherwise create problems with acoustic standing waves.

To block sound transmission, you need to make the structure all of these:
1) Airtight
2) With lots and lots of mass between the source and the target of the sound
3) With Breaks in the structural path (such as rubber grommets or similar) to dampen vibration from passing from one area to another
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VAPORIZER WHOLESALE

[thethingwiththestuff]

yeah, i'm right with you. this is how i feel i addressed those concerns:

the window and bass absorper would be sealed airtight. also, this type of bass absorber works on the principle that the front panel does resonate, but is then stopped by the air gap, insulation, and the back of the box, i believe.

it wont be a hell of a lot of mass, but it will be several "leaves" (right?) for the sound to pass through. this is a stone, foundational, basement wall, not drywall. i just need to cut down some noise, not make it 100% soundproof. surely this would be better than nothing, yes? maybe i could stick some pucks on the back corners of the box against the window.

i'm hoping the box kills some at least hi mid (most annoying) transmission to the outside and provides some absorbption inside.

[philbo]

Well, what I was trying to get at was that ultimately, only you know enough about it to decide what will help you... For example, if your walls are drywall/studs/siding but have no insulation inside, it may not help much to soundproof the windows.

It sounds like you are on the right track overall.

I don't think that bass traps will do much for transmission though. They are put into corners and against walls because they work by absorbing both incident and reflected bass. For bass to be reflected, it has to be passing through the trap. (I might be wrong on this... I'd suggest asking Ethan Winer what he thinks.)
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ZX14 VS HAYABUSA

[thethingwiththestuff]

word......seems like we're on the same page. hopefully ethan will chime in! i should post pictures, i suppose. your point about reflection and catching the bass as it passes through the trap once and again on its return trip sounds right and does give me pause, though.

i guess you could say i'm only trying to maim to birds with one stone, and if i end up killing them, i'll feel lucky. as if that makes any sense....

[Ethan Winer]

> hopefully ethan will chime in! <

Did I hear my name?

I'm not much of an isolation expert, but I do know that for a fixed amount of "wall" thickness, having multiple "leaves" is bad for isolation, not good.

--Ethan

[thethingwiththestuff]

hmm...noted. i got some more reading to do. thanks all.

[bpape]

To me, you're operating at cross odds when you are trying to isolate the outside via the window but then you build a resonator on top of it. The basic plan is good but skip the resonator.

- fill the cavity with absorbtion to absorb sound AND to damp the window vibrations.

- Use a small frame around the window and caulk it up. Try to give yourself at least 4", 6" is better. Make sure your absorbtion fills the cavity all the way to the edge of the frame.

- (here's the change), use 2 layers of 3/4" MDF screwed onto that frame. This will NOT resonate much (and you don't want it to) and the mass is so high, coupled with the deep cavity, will drive the resonant frequency much lower than the walls surrounding the window.

Bryan

[thethingwiththestuff]

thanks much, bryan, i like it. as the walls are thick stone, i doubt the resonant frequency will be lower than the walls, but yeah, that sounds great.

my second purpose for covering the panel with wood is to get some high end reflection to liven the room up a little as i flatten out the low mid and bass response. it sounds a little too dry right now. any recommendations for something other than MDF to achieve that, or might that be sufficient? can you paint/seal MDF or is there a reason i wouldn't want to paint whatever covers the box?

thanks again.

[bpape]

You can certainly paint it. Not sure what you're going to use to be more reflective than MDF (or the glass that was there for that matter!). Sounds like other things in the room are going to need to be addressed.

(...and yes, the stone wall will likely be a lower resonance....)

Bryan

[thethingwiththestuff]

i hear you. thanks a lot! i will post pictures/samples when i finish.